As a prior-art hybrid construction machine, those performing energy regenerations by rotating a hydraulic motor using working oil led from a hydraulic cylinder is known.
JP2011-179541A discloses a hybrid construction machine provided with a boom cylinder vertically rotating a boom. In this hybrid construction machine, a hybrid motor is rotated by using working oil returned from the boom cylinder when the boom is lowered, and a power generator is driven by a rotating torque of the hydraulic motor.